Is it possible to obtain the bind parameters created from a POST Body with content type x-www-form-urlencoded as a collection?

I'm faced with a problem with one of my update procedure's Resource Template. Our application is dynamic in that data instances are defined by metadata in other tables,
I am attempting to update a record but do not know until time of processing what :bind variables will be available.

An example of our POST request is like:

POST my_api/instances/12345
Content Type: x-www-form-urlencoded

Post body: 234=John&235=Watson&236=Male

Where 234 is a user defined First Name field saved in the metadata tables and is listed as a child of 12345.